As energy costs increase and the use of electric lighting and motors expands, more and more attention is being given to the design of efficient electrical systems. In today's environment of power conservation, power reduction systems are available to make reductions in available line power for subsequent application to varied loads, such as lighting systems. One such example is described in U.S. Pat. No. 6,525,490 for Power Saving Circuitry. However, synchronization of the power reduction systems can become problematic for experienced variations in line power frequency.
In practice the nominal frequency is raised or lowered by a specific percentage to maintain synchronization. In the synchronous grid of Continental Europe, the deviation between network phase time and UTC is calculated at 08:00 each day in a control center in Switzerland, and the target frequency is then adjusted by up to ±0.02% from 50 Hz as needed. In North America, whenever the error exceeds 10 seconds for the east, 3 seconds for Texas, or 2 seconds for the west, a correction of ±0.02 Hz (0.033%) is applied. The trend in system frequency is a measure of mismatch between demand and generation, and so is a necessary parameter for load control in interconnected systems. During a severe overload caused by tripping or failure of generators or transmission lines the power system frequency will decline, due to an imbalance of load versus generation. Loss of an interconnection, while exporting power (relative to system total generation) will cause system frequency to rise. Temporary frequency changes are an unavoidable consequence of changing demand. Exceptional or rapidly changing mains frequency is often a sign that an electricity distribution network is operating near its capacity limits, dramatic examples of which can sometimes be observed shortly before major outages.
Further, it is recognised that for smaller power systems, such as for emergency building generators, may not maintain frequency with the same degree of accuracy for larger power generation networks.
Further, it is recognised other variations can occur in line power, such as voltage/current fluctuation due to noise introduced into the supply line, which can affect synchronization between power reduction equipment and the line power.